Emerging Water-Borne Pathogens
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Appl Microbiol Biotechnol (2003) 61:424–428 DOI 10.1007/s00253-003-1302-y MINI-REVIEW S. Sharma · P. Sachdeva · J. S. Virdi Emerging water-borne pathogens Received: 1 October 2002 / Revised: 27 February 2003 / Accepted: 28 February 2003 / Published online: 9 April 2003 Springer-Verlag 2003 Abstract Emerging water-borne pathogens constitute a number of reviews and other publications available on the major health hazard in both developed and developing subject discuss emerging and re-emerging pathogens in nations. A new dimension to the global epidemiology of general, including water-borne, without addressing the cholera—an ancient scourge—was provided by the issues specifically pertinent to emerging water-borne emergence of Vibrio cholerae O139. Also, water-borne pathogens. This review critically examines which organ- enterohaemorrhagic Escherichia coli (E. coli O157:H7), isms really qualify as emerging water-borne pathogens, although regarded as a problem of the industrialized west, the possible reasons underlying their emergence and has recently caused outbreaks in Africa. Outbreaks of specific measures to face the challenge posed by them. chlorine-resistant Cryptosporidium have motivated water Due to the paucity of data, it may be difficult to decide authorities to reassess the adequacy of current water- which of all water-borne pathogens are emerging. Nev- quality regulations. Of late, a host of other organisms, ertheless, there are some clear-cut candidates. such as hepatitis viruses (including hepatitis E virus), No organism other than Vibrio cholerae could serve as Campylobacter jejuni, microsporidia, cyclospora, Yersin- a better example of an emerging water-borne pathogen. ia enterocolitica, calciviruses and environmental bacteria Cholera is an ancient scourge and to date seven like Mycobacterium spp, aeromonads, Legionella pneu- pandemics have been recorded. Of the several recognized mophila and multidrug-resistant Pseudomonas aerugi- serogroups, V. cholerae O1 has been responsible for these nosa have been associated with water-borne illnesses. pandemics. In 1992 however, a new strain called V. This review critically examines the potential of these as cholerae O139 Bengal appeared in South India and emerging water-borne pathogens. It also examines the caused explosive outbreaks of cholera-like disease (Ra- possible reasons, such as an increase in the number of mamurthy et al. 1993). In a matter of one year, the new immunocompromised individuals, urbanization and hor- strain spread to several parts of India and to neighbouring izontal gene transfer, that may underlie their emergence. Bangladesh and Thailand (Nair et al. 1994). By the end of Further, measures required to face the challenge posed by 1993, cholera outbreaks due to V. cholerae O139 were these pathogens are also discussed. reported from South Asia and other countries of the world. Soon after its appearance, V. cholerae O139 outnumbered V. cholerae O1 and became the dominant serogroup in India and other parts of the Indian sub- Emerging water-borne pathogens continent. It was thought that this was probably the beginning of a new pandemic—the eighth pandemic of In 1992, the Institute of Medicine described an emerging cholera (Nair et al. 1996). But, by 1994, there was a infection as any new, re-emerging, or drug-resistant dramatic decrease in V. cholerae O139 and once again V. infection whose incidence in humans has increased within cholerae O1 became the dominant species. It is thought the past two decades or whose incidence threatens to that, in the years to come, V. cholerae O139 is going to increase in the near future (Lederberg et al. 1992). A play an important role in the global epidemiology of cholera (Garg et al. 1998). S. Sharma · P. Sachdeva · J. S. Virdi ()) Following identification of the O139 serogroup and the Microbial Pathogenicity Laboratory, Department of Microbiology, finding that environmental, non-toxigenic strains may University of Delhi South Campus, play an important role in the evolution of toxigenic V. Benito Juarez Road, 110 021 New Delhi, India cholerae (Karaolis et al. 1995), there has been a lot of e-mail: [email protected] interest in the study of non-O1, non-O139 serogroups. At Tel.: +91-11-26879950 least three localized outbreaks of diarrhoea caused by Fax: +91-11-26885270 425 non-O1, non-O139 serogroups have been described in the enzie et al. 1994). The oocysts of Cryptosporidium are recent literature. These include an outbreak caused by V. resistant to the microbiocidal concentrations of chlorine cholerae O10 and O12 in February 1994 in Lima, Peru normally used for the disinfection of drinking water. Like (Dalsgaard et al. 1995), another caused by O10 in Delhi, E. coli O157:H7, Cryptosporidium has also been regarded India (Rudra et al. 1996) and an epidemic caused by as a problem in the developed countries. Nevertheless, the stable toxin producing non-O1 V. cholerae among organism has been isolated from the stools of diarrhoeic Khmers in a camp in Thailand (Bagchi et al. 1993). In patients in developing countries (Nath et al. 1999). 1996, an inexplicable upsurge in the incidence of non-O1, However, nothing is known about the prevalence of this non-O139 V. cholerae infections was observed among pathogen in the environmental waters of developing hospitalized patients in Kolkata, India, which even nations, which needs to be studied. Other enteric proto- outnumbered the O1 and O139 serogroups (Sharma et zoa, like microsporidia and cyclospora, have been al. 1998). Although non-O1, non-O139 V. cholerae are detected in surface, ground and treated wastewaters, not regarded as important enteropathogens currently, their indicating their potential as water-borne pathogens. They increasing incidence suggests their potential as important have been recognized as gastrointestinal pathogens with future water-borne pathogens. increasing frequency since the AIDS epidemic. However, Pathogenic Escherichia coli, such as enteroinvasive E. microsporidia have also been implicated as pathogens in coli, enteropathogenic E. coli, enteroaggregative E. coli otherwise healthy individuals (Goodgame 1996). Further and shiga toxin-producing E. coli (STEC), constitute a research is required to understand the distribution and very large and important group of water-borne pathogens. survival of microsporidia and cyclospora in aquatic STEC and particularly E. coli O157:H7 (also called as environments, so that their true potential as emerging enterohaemorrhagic E. coli or EHEC) have been associ- water-borne pathogens may be evaluated. ated clinically with presentations ranging from asymp- Campylobacters are becoming increasingly important tomatic infection to severe bloody diarrhoea, which may as the cause of acute gastroenteritis in both industrialized lead to life-threatening sequelae, such as haemolytic and developing nations. During recent years, an increas- uraemia syndrome. This organism, although primarily ing incidence of campylobacteriosis has been reported in associated with food-borne outbreaks, has also become an many developed countries (Shane 2000). Although important public health concern as a water-borne patho- mainly food-borne, water is also regarded as an important gen. Water-borne E. coli O157:H7 outbreaks due to route for the transmission of campylobacters. Most of the drinking water (Dev et al. 1991; Swerdlow et al. 1992) cases are sporadic, although large water-borne outbreaks and recreational water exposure have been reported have also been reported. Between 1992–1996, six (Brewster et al. 1994; Keene et al. 1994). A large outbreaks of campylobacteriosis occurred in Sweden epidemic of haemorrhagic colitis in Africa was also (Furtado et al. 1998). Two water-borne outbreaks of this reported to be a water-borne outbreak of E. coli O157:H7 organism were reported in Central Norway in 1994 and (Isaacson et al. 1993). Although generally considered to 1995. Recently, a water-borne Campylobacter jejuni be a problem in the developed nations, STEC have outbreak was reported from a Danish town due to recently been isolated from developing countries (Dutta et contamination of the water supply with ground water al. 2000; Khan et al. 2002a, 2002b). These isolates have (Engberg 1998). been obtained from either cattle or diarrhoeic human Yersinia enterocolitica, an important food- and water- subjects, both of which can act as sources for water-borne borne bacterium is known to cause a variety of gastro- E. coli O157:H7. The non-O157 verotoxin-producing intestinal problems. Most commonly, it causes acute strains are also transmitted by water (Chalmers et al. diarrhoea, terminal ileitis and mesenteric lymphadenitis. 2000) and need to be studied more intensively (Goldwater Post-infectious sequelae are manifested in the form of and Bettelheim 1998). Efficient methods to detect STEC, reactive arthritis. World-wide surveillance data on Y. including E. coli O157:H7, in water have been reported enterocolitica show great changes over the past two recently (De Boer and Heuvelink 2000), which would be decades and bring forth its emerging nature (Ostroff extremely useful in studying the prevalence of this 1995). The strains present in the aquatic environment are organism in water. extremely heterogeneous, belonging to biotype 1A. It has Cryptosporidium, a coccidian parasite, causes persis- been shown that biotype 1A strains of Y. enterocolitica tent diarrhoea (cryptosporidiosis) in immunocompro- may be pathogenic by some novel mechanisms. Thus, the mised